Method of bonding diamond and metal



June 1968 H. L. STRAUSS, JR

METHOD OF BONDING DIAMOND AND METAL Filed Oct. 8, 1963 FIG.

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United States Patent Ofice 3,339,981 Patented June 25, 1968 3,389,981METHOD OF BONDING DIAMOND AND METAL Harry L. Strauss, Jr., 183 SterlingRoad, Harrison, N.Y. 10528 Filed Oct. 8, 1963, Ser. No. 314,720 Claims.((31. 51293) This invention relates to the bonding of diamond and metal,and more particularly to the manufacture of abrasive tools using diamondgrit or pieces.

In some tools diamond grit may be distributed through a body of matrixmaterial, and in other cases using somewhat larger pieces, the diamondsmay be localized at the surface of the tool. One example is a dressingtool having diamond grit for dressing abrasive wheels using siliconcarbide, aluminum oxide or other such abrasive. The dressing tool may bea rod or a wheel. A wheel having diamond grit may itself be used as anabrasive wheel. Another example would be a core bit for drilling forearth exploration, in which a tubular matrix with diamonds embedded inits lower edge is used.

Ditferent processes have been used, including casting metal around thediamonds, which is bad because of oxide between the metal and diamondwhich is injurious to the bond. Souventional brazing has been used, butthis needs flux to wet both metal and diamond, and the flux detractsfrom the bond. Hydrogen brazing is better than in air, but is veryexpensive because of equipment needed, and it is difiicult to obtainuniform results. There is also danger of hydrogen explosion.

Sintered metal powder has been used. In one system the sintering is donein a hydrogen atmosphere, but this raises all of the hydrogen problemsalready mentioned. In another system there is sintering in air, using ahot press, but this again forms oxides. Sintering with a hot press in avacuum, or in hydrogen, has been suggested, but again complex equipmentis needed and difiiculties arise.

The primary object of the present invention is to overcome the foregoingdifficulties, and to generally improve the manufacture of diamond toolsof the described class. Another object is to provide a process whichresults in a greatly improved diamond tool by achieving a true metal todiamond bond, which holds the diamond with maximum strength. There isalso a better metal to metal bond. In both cases there is probably abetter wetting action.

To accomplish the foregoing general objects, and other more specificobjects which will hereinafter appear, my invention resides in theprocess steps, and their relation one to another, as are hereinaftermore particularly described in the following specification. Thespecification is accompanied by drawings in which:

FIG. 1 is a front elevation of a dressing or abrasive wheel;

FIG. 2 is a section through the same;

FIG. 3 is a schematic transverse section through a treatment chamberused in practicing the invention; and

FIG. 4 is a schematic perspective view showing the treatment chamberconnected to high vacuum apparatus.

Referring to the drawing, and more particularly to FIGS. 1 and 2, theparticular tool here being made is a small dressing or abrasive wheel12, using diamond grit in a matrix of sintered metal. However, asexplained above, the tool may take a variety of forms depending on thepurpose for which it is intended.

In accordance with known practice, the mixture preliminarily iscompressed under sufiicient pressure to give it some green strength, sothat the embryo product may be more conveniently handled.

Referring now to FIG. 4 of the drawing, there is a high vacuum chamber14, which in this case is cylindrical and has a hinged door 16 at oneend. Appropriate gaskets are provided to permit exhaustion to a highvacuum. The vacuum may be produced by any known controlled high vacuumapparatus, indicated in somewhat simplified or schematic form at 18 and20, the connection to chamber 14 being through a relatively largediameter pipe 22. A ram 24 projects downwardly through the wall of thevacuum chamber, and is actuated by a press which is not shown. The useof ram 24 is optional, and when it is employed, it passes throughelaborate seals of known character so as not to prevent high vacuum inthe chamber.

Referring now to FIG. 3 of the drawing, the chamber 14 and ram 24correspond to those previously mentioned. The chamber rests on a base26, which in turn rests on the bed of the press (not shown) whichactuates the ram 24. The chamber 14 includes a table 28 having apedestal 34) on which the embryo product may be carried, this beingindicated at 12. The product includes a metal hydride, for release ofhydrogen during the process. The chamber 14 has means to heat theproduct to a high temperature, and in the present case the heat isprovided by an induction heating coil 32 which may be of conventionalcharacter. Usually it has turns of copper tubing which carry water forcooling. The coil could be movable, but more simply may be fixed inlocation but so dimensioned as to afford easy access to the productbeing treated. The vacuum chamber 14 is further arranged for very rapidcooling by refrigeration, and for this purpose, the chamber is linedwith refrigerator coils indicated at 36. It will be understood that theinduction heating coil 32 is connected through suitable leads or pipesto a source of electrical power, not shown, and the coils 36 areconnected through pipes 38 to suitable refrigerating equipment, notshown.

While not essential, it is preferred to treat the product 12 underdirect mechanical pressure at the same time that it is being subjectedto environmental vacuum, and for this purpose the product may be placedin a bottom mold 411, and enclosed by a top mold 42, the latterreceiving the force of ram 24 when the ram is lowered. The ram isretractable for a substantial distance to facilitate insertion orremoval of the mold, and/or the product being treated.

The chamber preferably has a temperature-sensitive device 44 which leadsthrough connection 46 to a temperature indicator, and apressure-sensitive device 48 which leads through connection 50 to avacuum indicator.

The vacuum chamber is further provided with a small crucible 52 in whicha suitable getter is placed. For the particular procedure hereinafterdescribed, the getter is preferably small chips of titanium, or smallpieces of titanium wire, indicated at 54. The amount of titanium gettermay be about two percent of the matrix material being treated.

The metal powder mixture in the matrix, 32 may contain some or all ofiron, copper, tin. nickel, cobalt, chromium boride, tungsten carbide,and titanium hydride. The constituents may vary, and also theproportions used may vary.

Titanium hydride or some metal hydride is highly important in themixture because it releases hydrogen. which is valuable as a reducingagent and to help the vacuum remove contaminants. In one theory, thepure titanium getter in the crucible adsorbs hydrogen and then exchangesit for other contaminants at an elevated temperature. Most of thecontaminants and hydrogen are removed by the vacuum, and the getterimproves the operation of the apparatus.

The present invention may be considered to be empirical, and I do notwish to be limited to or to be bound by this or other theoreticalobservations in this description.

The process of manufacture includes subjecting the product to heat andto environmental vacuum until the temperature has risen high enough andthe treatment is continued long enough for the release and removal ofhydrogen and impurities, and for bonding of the metal, whereupon theheating is replaced by abrupt cooling by actual refrigeration until theproduct is cooled to room temperature. It is possible that this form ofquench action produces a precipitation hardening of the metal. In anycase the result is an improved product. During this cooling theenvironmental vacuum is maintained. The temperature to which the productis raised is preferably in a range of from 1800 to 2400. The vacuum ispreferably carried down to about 10- or microns of mercury. Thetreatment is continued for a period of about six to ten minutes, butpreferably in several stages, as is described later.

In preferred method, the product is subjected to direct mechanicalpressure during the treatment described above. When this is to be doneit is not essential to previously cold compress the material for greenstrength as mentioned above. However it is still convenient anddesirable to do so.

As mentioned, the treatment is preferably divided into stages, and inthe first stage the temperature may be raised to above 800 F., and theproduct is treated at that temperature for several minutes, say three tofive minutes. Hydrogen is released from titanium hydride at about 700F., and it is desired to safely reach that temperature. Then the heatingmay be resumed to raise the temperature to a range of from 1800 to 2400F, and

the product then is treated at the said elevated temperature for severalminutes, say three to five minutes.

Considering the preferred process in greater detail, the vacuumapparatus and the heater may be operated and the temperature raised to arange of 400 to 500 F. Active evacuation is then interrupted, whilecontinuing heating to a temperature of say 800 F., at which point theexisting conditions are maintained for several minutes, say three tofive minutes, as mentioned above. The operation of the heater is resumedto raise the temperature to a range of 1800 to 2300 F. During this timeactive evacuation is resumed down to a vacuum of about 10- or 10-microns of mercury, but the restart of the vacuum apparatus may bedelayed, but if delayed it should be started at latest when thetemperature has reached 1600 F.

The final temperature selected depends on whether the metal matrix ismade of a soft or hard metal, the lower temperature (say 1800 F.) beingused for softer metals, and the higher temperature (say 2300 F.) beingused for harder metals. By hard metal is meant metals such as tungstencarbide, or chromium bon'de or other borides with suitable cementingmetals. By soft metal is meant nickel bearing brasses, or copper alloys.

The elevated temperature is maintained for a period of several minutes,say three to five minutes, this being the second treatment stage. Duringthis time the vacuum apparatus may be stopped or not, depending on thealloy being treated, and the getter being used. The temperature then maybe momentarily raised a little, say F. higher, but this is notessential.

The energization of the induction coil then is stopped, andrefrigeration is applied to the refrigerating coils for abrupt cooling.Here again there is preferably a difference in procedure as between hardand soft metals. In the case of hard metals, the vacuum apparatus, ifstopped during the second stage dwell, now is started and operatesthroughout the refrigeration or rapid cooling period. In the case ofsoft metals the starting of the vacuum apparatus is delayed until thetemperature has dropped to about 900 F. and is then started. In eithercase (hard or soft metals) the active evacuation is applied during thecontinued rapid cooling or refrigeration below 900 F. and on down toroom temperature.

Both the vacuum apparatus and the refrigerator are stopped beforeopening the vacuum chamber door, and the ram is raised for removal ofthe finished product.

When mechanical pressure is applied by means of a ram during treatment,as here shown, the mold parts are designed to withstand the hightemperature, and also the abrupt drop in temperature caused byrefrigeration. The mold 40 and ring 42 constituting the mold arepreferably made of carbon, but may be made of a refractory material, orof stainless steel. Carbon is preferably used when the sintered metal isone which is rather nonresponsive to induction heating. The carbon thenheats up and transfers heat to the product being treated. If the matrixmaterial is responsive to induction heating the product itself isheated, and the mold may be made of refractory material, or of stainlesssteel. The ram is also made of refractory material or of stainlesssteel.

When mechanical pressure is not used in the vacuum chamber the wheel ispreliminarly compressed cold, and simply rests on pedestal 30 within theinduction coil. The wheel is directly heated by the induction coil.

It is believed that my improved method of bonding diamond and metal, aswell as the advantages of the same, will be apparent from the foregoingdetailed description. It will also be understood that while I havedescribed the invention in a preferred form, changes may be made withoutdeparting from the scope of the invention, as sought to be defined inthe following claims.

I claim:

1. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide and compressing the same to form an embryo abrasiveproduct having some green strength, subjecting the product to directmechanical pressure and to heat and to environmental vacuum in thepresence of a titanium getter until the temperature has risen to a rangeof 1800 to 2400 F. and the treatment has continued for about six to tenminutes, and thereupon terminating the heating and abruptly cooling byrefrigeration while maintaining the direct mechanical pressure and theenvironmental vacuum until the product is cooled to approximately roomtemperature.

2. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide and compressing the same, subjectng the product to heatand to environmental vacuum until the temperature reaches about 800 F.,treating the product at that temperature for several minutes, continuingevacuation down to a vacuum of about 10- to 10- microns of mercury andat the same time resuming heating to raise the temperature to a range offrom 1800" to 2400 F., treating the product at the said elevatedtemperature for several minutes, and terminating the heating and veryabruptly cooling the product by refrigeration down to approximately roomtemperature.

3. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide, and including also a metal hydride, and compressingthe same, subjecting the product to heat and to environmental vacuumuntil the temperature reaches about 800 F., terminating activeevacuation and treating the product at that temperature for about threeto five minutes, resuming active evacuation down to a vacuum of about10- to 10 microns of mercury and at the same time resuming heating toraise the temperature to a range of from 1800 to 2400 F., terminatingactive evacuation and treating the product at the said elevatedtemperature for a period of about three to five minutes, and thereuponresuming evacuation and very abruptly cooling the product byrefrigeration down to approximately room temperature.

4. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide and compressing the same, subjecting the product toheat and to environmental vacuum until the temperature reaches a rangeof 400 to 500 F., terminating active evacuation and continuing heatingto a temperature of about 800 F., treating the product at thattemperature for several minutes, resuming active evacuation down to avacuum of about l to microns of mercury and at the same time resumingheating to raise the temperature to a range of from 1800 to 2400" F.,depending on whether the metal is soft or hard respectively, treatingthe product at the said elevated temperature for several minutes, andvery abruptly cooling the product *by refrigeration down toapproximately room temperature.

5. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide tin, nickel, cobalt, chromium boride, and tungstencarbide, and including also a metal hydride, and compressing the same,subjecting the product to heat and to environmental vacuum until thetemperature reaches a range of 400 to 500 F., terminating activeevacuation and continuing heating to a temperature of about 800 F.,treating the product at that temperature for about three to fiveminutes, resuming active evacuation down to a vacuum of about 10- to 10-microns of mercury and at the same time resuming heating to raise thetemperature to a range of from 1800 to 2400 F., depending on whether themetal is soft or hard respectively, terminating active evacuation andtreating the product at the said elevated temperature for a period ofabout three to five minutes, thereupon resuming evacuation for hardmetals but not for soft metals and at the same time and in either caseterminating the heating and very abruptly cooling the product byrefrigeration down to a temperature of about 900 F., and continuing theevacuation for hard metals or resuming evacuation for soft metals whilecontinuing the abrupt cooling down to approximately room temperature.

6. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide and compressing the same to form an embryo abrasive,

product having some green strength, subjecting the prodnot to directmechanical pressure and to heat and to ening to raise the temperature toa range of from 1800 to 2400 F., treating the product at the saidelevated temperature for several minutes, and terminating the heating.

and very abruptly cooling the product by refrigeration down toapproximately room temperature.

7. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide, and including also a metal hydride, and compressingthe same to form an embryo abrasive product having some green strength,subjecting the product to direct mechanical pressure and to heat and toenviron-mental vacuum in the presence of a titanium getter until thetemperature reaches about 800 F., treating the pnoduct at thattemperature for about three to five minutes, continuing down to a vacuumof about 10- to 10- microns of mercury and at the same time resumingheating to raise the temperature to a range of from 1800 to 2400 F.,terminating active evacuation and treating the product at the saidelevated temperature for a period of about three to five minutes, andthereupon resuming evacuation and very abruptly cooling the product byrefrigeration down to approximately room temperature.

8. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide and compressing the same to form an embryo abrasiveproduct having some green strength, subjecting the product to directmechanical pressure and to heat and to environmental vacuum in thepresence of a titanium getter until the temperature reaches a range of400 to 500 F., terminating active evacuation and continuing heating to atemperature of about 800 F., treating the product at that temperaturefor several minutes, resuming active evacuation down to a vacuum ofabout 10- to 10 microns of mercury and at the same time resuming heatingto raise the temperature to a range of from l800 to '2400 F., dependingon whether the metal is soft or hard respectively, treating the Productat the said elevated temperature for several minutes, and very abruptlycooling the product by refrigeration down to approximately roomtemperature.

9. The method of bonding diamond pieces and metal which includesembedding the diamond pieces in a metal powder selected from the groupconsisting of iron, copper, tin, nickel, cobalt, chromium boride, andtungsten carbide, and including also a metal hydride, and compressingthe same to form an embryo abrasive product having some green strength,subjecting the product to direct mechanical pressure and to heat and toenvironmental vacuum in the presence of a titanium getter until thetemperature reaches a range of 400 to 500 F., terminating activeevacuation and continuing heating to a temperature of about 800 F.,treating the product at that temperature for about three to fiveminutes, resuming active evacuation down to a vacuum of about 10 to 10*microns of mercury and at the same time resuming heating to raise thetemperature to a range of from 1800 to 2400 F., depending on whether themetal is soft or hard respectively, terminating active evacuation andtreating the product at the said elevated temperature for a period ofabout three to five minutes, thereupon resuming evacuation for hardmetals but not for soft metals and at the same time and in either caseterminating the heating and very abruptly cooling the product byrefrigeration down to a temperature of about 900 F., and continuing theevacuation for hard metals or resuming evacuation for soft metals whilecontinuing the abrupt cooling down to approximately room temperature.

10. The method of bonding diamond pieces and metal which includespreliminarily embedding the diamond pieces in a metal powder selectedfrom the group consisting of iron, copper, tin, nickel, cobalt, chromiumboride, and tungsten canbide, and including also a metal hydride,

7 and compressing the same to form an embryo article hav- ReferencesCited ing some green strength," subjecting the product to heat UNITEDSTATES PATENTS and vacuum until the temperature reaches a range or 400to 500 F., shutting off the evacuation without ad- 2,240,329 5/1941Bevlufll'd 51309 mitting air and heating to a temperature of about 800 52,396,015 3/1946 Lidefl et 51309 F., treating the product at thattemperature for several 2, l /1955 Hall 51309 minutes, resuming heatingand evacuation to raise the tem 2,737,454 3/ 1956 Danec 51309 peratureto a range of from 1800 to 2400 F, and ter- 3,178,273 4/1965 Libal 51309minating the heating and very abruptly cooling by refrigeration down toapproximately room temperature. DONALD ARNOLD, P rimaly Examine"-

1. THE METHOD OF BONDING DIAMOND PIECES AND METAL WHICH INCLUDESEMBEDDING THE DIAMOND PIECES IN A METAL POWDER SELECTED FROM THE GROUPCONSISTING OF IRON, COPPER, TIN, NICKEL, COBALT, CHROMIUM BORIDE, ANDTUNGSTEN CARBIDE AND COMPRESSING THE SAME TO FORM AN EMBRYO ABRASIVEPRODUCT HAVING SOME "GREEN STRENGTH," SUBJECTING THE PRODUCT TO DIRECTMECHANICAL PRESSURE AND TO HEAT AND TO ENVIRONMENTAL VACUUM IN THEPRESENCE OF A TITANIUM GETTER UNTIL THE TEMPERATURE HAS RISEN TO A RANGEOF 1800* TO 2400*F. AND THE TREATMENT HAS CONTINUED FOR ABOUT SIX TO TENMINUTES, AND THEREUPON TERMINATING THE HEATING AND ABRUPTLY COOLING BYREFRIGERATIN WHILE MAINTAINING THE DIRECT MECHANICAL PRESSURE AND THEENVIRONMENTAL VACUUM UNTIL THE PRODUCT IS COOLED TO APPROXIMATELY ROOMTEMPERATURE.